Ink jet recording records an image or text on a recording sheet such as a paper sheet, applying various principles. This recording method has advantages in providing a relatively high speed recording, low noise and easy color image formation. There have been problems in maintenance or ink clogging of nozzles in this method, but improvements have been made in the ink and related device, and this method has been widely applied to various fields such as printers, facsimile devices and computer terminals.
It is required for ink recording sheet to accept printing dots at high density and bright image tone, to provide rapid ink absorption property producing no ink diffusion or blur in overlapped printed dots, and to provide printing dots with smooth periphery and no blurring in which printing ink is not so greatly diffused.
In recording sheets slow in ink absorption, two or more kinds of color ink drops repel one another at overlapped ink recording portions on the sheet, resulting in image unevenness, or different color inks at different but adjacent ink recording portions on the sheet are diffused and mixed, resulting in deterioration of image quality. Therefore, a recording sheet having high ink absorption property is eagerly sought.
Many techniques have been proposed in order to solve the above described problems.
There have been proposed, for example, an ink jet recording sheet paper of low size content wetted with surface treatment coating disclosed in Japanese Patent O.P.I. Publication No. 52-53012, an ink jet recording sheet paper comprising a support and provided thereon, an ink absorption layer disclosed in Japanese Patent O.P.I. Publication No. 55-5830, an ink jet recording sheet paper comprising a layer containing non-colloidal silica powder as pigment disclosed in Japanese Patent O.P.I. Publication No. 56-157, an ink jet recording sheet paper comprising an inorganic and organic pigment disclosed in Japanese Patent O.P.I. Publication No. 57-107878, an ink jet recording sheet paper comprising two void distribution peaks disclosed in Japanese Patent O.P.I. Publication No. 58-110287, an ink jet recording sheet paper comprising two upper and lower porous layers disclosed in Japanese Patent O.P.I. Publication No. 62-111782, an ink jet recording sheet paper comprising amorphous cracks disclosed in Japanese Patent O.P.I. Publication Nos. 59-68292, 59-123696 and 60-18383, an ink jet recording sheet paper comprising a fine powder layer disclosed in Japanese Patent O.P.I. Publication Nos. 61-135786, 61-148092 and 62-149475, an ink jet recording sheet paper comprising pigments or fine particle silica each having a specific physical property disclosed in Japanese Patent O.P.I. Publication Nos. 63-252779, 1-108083, 2-136279, 3-65376 and 3-27976, an ink jet recording sheet paper comprising fine particle silica such as colloidal silica disclosed in Japanese Patent O.P.I. Publication Nos. 57-14091, 60-219083, 60-210984, 61-20797, 61-188183, 5-278324, 6-92011, 6-183134, 7-137431 and 7-276789, or an ink jet recording sheet paper comprising hydrated alumina fine particles disclosed in Japanese Patent O.P.I. Publication Nos. 2-276671, 3-67684, 3-215082, 3-251488, 4-67986, 4-263983 and 5-16517.
An ink receiving layer, if it is a layer (hereinafter referred to as a void layer) having many voids to absorb or support ink, has good ink absorption property and provides high image quality with no blurring.
The void volume occasionaly changes during storage under high temperature and high humidity, and the void layer preferably contains solid fine particles to keep the void volume constant.
It is necessary that, in order to obtain a stable void layer containing solid fine particles, a hydrophilic binder be incorporated in the void layer. However, if the addition amount of the hydrophilic binder is too large relative to that of the solid fine particles, it has problems in that the hydrophilic binder fills spaces formed among the solid fine particles or swells at initial ink absorption to fill voids in the void layer and results in deterioration of ink absorption. Accordingly, the addition amount of the hydrophilic binder is limited.
The present inventors have made an extensive study and have found that the addition amount ratio by weight of the hydrophilic binder to the solid fine particles is necessary to be about 2 to 200. However, a high addition amount ratio of the solid fine particles brings about layer brittleness, and fine cracks occur on the ink absorption layer surface, particularly during storage under low humidity. When ink jet recording ink is provided on the recording sheet having such high addition amount ratio of the solid fine particles, the recording ink diffuses along the cracks occurred, resulting in serious deterioration of image quality.